Bernhoff, Hans

Abstract [en]

The introduction of electric and hybrid vehicles will make it possible to reduce the negative environmental impact from the transportation sector. The integration of a flywheel as a power handling device would enhance the efficiency of the electric driveline. This article presents a model for a proposed driveline with an integrated flywheel. It also compares the performance for that driveline with that of a driveline without a flywheel by simulating the model performing two different drive cycles, the American FTP 75 and the European NEDC. Simulations show that the integrated flywheel driveline enables higher energy density batteries, decreases total losses, increases the efficiency and lifetime of the battery and also enables an efficient regenerative braking.

Lundin, Johan

Abstract [en]

Energy storage is a crucial condition for both transportation purposes and for the use of electricity. Flywheels can be used as actual energy storage but also as power handling device. Their high power capacity compared to other means of storing electric energy makes them very convenient for smoothing power transients. These occur frequently in vehicles but also in the electric grid. In both these areas there is a lot to gain by reducing the power transients and irregularities.

The research conducted at Uppsala university and described in this thesis is focused on an all-electric propulsion system based on an electric flywheel with double stator windings. The flywheel is inserted in between the main energy storage (assumed to be a battery) and the traction motor in an electric vehicle. This system has been evaluated by simulations in a Matlab model, comparing two otherwise identical drivelines, one with and one without a flywheel.

The flywheel is shown to have several advantages for an all-electric propulsion system for a vehicle. The maximum power from the battery decreases more than ten times as the flywheel absorbs and supplies all the high power fluxes occuring at acceleration and braking. The battery delivers a low and almost constant power to the flywheel. The amount of batteries needed decreases whereas the battery lifetime and efficiency increases. Another benefit the flywheel configuration brings is a higher energy efficiency and hence less need for cooling.

The model has also been used to evaluate the flywheel functionality for an electric grid application. The power from renewable intermittent energy sources such as wave, wind and current power can be smoothened by the flywheel, making these energy sources more efficient and thereby competitive with a remaining high power quality in the electric grid.